This invention relates generally to electrical systems of motor vehicles. More particularly, the invention relates to battery disconnect circuits for preventing battery drain when the engine does not run for extended periods of time.
Certain motor vehicles, heavy trucks that are powered by diesel engines for example, may be parked for extended periods of time. If its engine is allowed to keep running after a vehicle has been parked, the alternator should be effective to keep the battery bank charged. If the engine is shut down, either intentionally by the driver, or automatically by a device such as an idle shutdown timer, while the circuits for electric devices remain on, the battery bank will begin to drain. For example, an ignition switch will typically remain on after an idle shutdown timer has timed out, and certain circuits that are left on may continue to draw current.
Because the battery bank must be able to provide sufficient current for cranking the engine at starting, a diesel-powered heavy truck typically has a battery bank comprising multiple storage batteries ganged together in parallel. If the battery bank is allowed to drain to the point where it cannot deliver the large cranking current necessary for starting the engine, the vehicle cannot be operated. Because a heavy truck may be parked for an extended period of time, it is therefore appropriate to guard against the possibility that its battery bank will be drained due to failure to turn off all its electric circuits.
Consequently, it is known to place a disconnect switch in circuit between the battery bank and the rest of the vehicle electrical system. All that need be done to avoid inadvertent draining of the battery bank while a heavy truck is parked is to turn the disconnect switch off, an act that would typically be performed by the driver upon turning the engine off and departing the vehicle. Because of the particular placement of the disconnect switch in circuit, the disconnect switch is physically mounted at the battery box outside the truck cab. The driver can therefore turn the switch off and on only when he is outside the cab.
A typical installation for a disconnect switch involves the use of two heavy conductors, one to connect the battery terminal of the disconnect switch to a terminal of the battery bank, such as the positive terminal in a negative ground electrical system, and another to connect the load terminal of the disconnect switch to a distribution point for the entire electrical system load, including a cranking motor solenoid through which cranking current is delivered to the cranking motor. Such a distribution point may be a terminal on the cranking motor solenoid.
The present invention relates to disconnect switch circuits that are believed to offer better solutions for avoiding inadvertent battery draining when a vehicle is parked for an extended period of time. Rather than placing a disconnect switch in circuit between a battery bank and a distribution point for the entire electrical system load, the invention places the disconnect switch between the battery bank and a distribution point for the entire system load except the engine cranking motor. This allows the circuit between the battery bank and the contacts of a cranking motor solenoid that is energized to run the cranking motor to be switch-free. The cranking motor solenoid is often integrated with the cranking motor itself, rather than being a discrete component that is separate from the cranking motor so as to have a battery terminal connected by a heavy conductor to the ungrounded battery bank terminal and a load terminal connected by another heavy conductor to a terminal on the cranking motor. When the cranking motor solenoid is integrated with the cranking motor, the integrated assembly has a terminal connected to the ignition switch start contact, either directly or through a relay, and a terminal to which one termination of such a switch-free circuit is connected. Such a switch-free circuit, whether connected to a cranking motor solenoid that is separate from the cranking motor or one that is integrated with the cranking motor, provides important advantages.
Rather than using one or more heavy conductors from the ungrounded battery bank terminal to the disconnect switch and one or more heavy conductors from the disconnect switch to the cranking motor solenoid for connecting the ungrounded terminal of the battery bank to the cranking motor when the disconnect switch is placed between the battery bank and the cranking motor, the present invention provides a continuous, switch-free conduction path from the ungrounded battery bank terminal to the contacts of the cranking motor solenoid. Although the length of such a continuous, switch-free conduction path may possibly be slightly greater than the combined lengths of the separate conductors it replaces, the number of terminals at the conductor ends are reduced from four to two, and the number of fasteners needed is cut in half. And although an installation that uses the invention may require an extra conductor and associated fasteners from the load distribution point to the battery terminal of the disconnect switch, that cable need not be as heavy as the one from the battery bank to the cranking motor because it does not have to be sized to also carry the amperage of the cranking motor current.
Another advantage of removing the disconnect switch from the battery feed to the cranking motor solenoid is that the electrical resistance between the battery bank and the cranking motor solenoid is significantly reduced. A switch-free path eliminates the contact resistance that is inherently present in a switch. And although some might consider that resistance small, it is significant when the large amperage of the cranking current is considered. Large current flowing through even a small resistance creates a non-trivial voltage drop and attendant heating. Avoidance of such losses is believed especially significant and beneficial when one recognizes the difficult task of starting a diesel engine, which is most noticeable in subzero weather.
Allowing the cranking motor to become a potential battery drain because of the placement of the disconnect switch in accordance with principles of the invention should have no serious adverse consequences because it is quite improbable the cranking motor solenoid circuit that energizes the cranking motor solenoid to operate the cranking motor will be inadvertently left on when the vehicle is parked and the engine turned off. First, operation of the cranking motor is quite likely to be noticed unless a person is totally deaf. Second, ignition switches that are presently in widespread use require maintained contact by the driver against a return spring force when placed in START position for cranking the engine. The return spring force will return the switch to IGNITION position, breaking the START feed, when the driver ceases the maintained contact.
The invention is therefore believed to provide a cost-effective improvement for avoiding unintended battery draining in a motor vehicle when parked for an extended period of time, and the possible inconvenience of having to jump-start the engine, to replace one or more batteries, or perhaps even to tow the vehicle.
One general aspect of the invention relates to an engine-powered land vehicle comprising a chassis containing an engine and a drivetrain through which the engine propels the vehicle on land. A body that provides a compartment for a driver of the vehicle is disposed on the chassis. The electrical system comprises a battery bank having one or more D.C. storage batteries, an electric cranking motor that draws current from the battery bank to crank the engine at starting when a cranking motor solenoid is energized, and a main control switch (commonly known as a ignition switch) that can be placed selectively in any one of multiple positions by the driver to selectively control the delivery of current from the battery bank to multiple circuit protection devices (typically fuses and circuit breakers) for distributing current to individual circuits in the vehicle, including a cranking motor solenoid circuit through which the cranking motor solenoid is energized. A disconnect switch is in circuit between the battery bank and the multiple circuit protection devices for selectively connecting and disconnecting the multiple circuit protection devices to and from the battery bank. A switch-free connection provides continuity between the battery bank and the cranking motor solenoid, both when the disconnect switch is connecting the multiple circuit protection devices to the battery bank and when the disconnect switch is disconnecting the multiple circuit protection devices from the battery bank. The switch-free connection carries current from the battery bank to a terminal of the cranking motor solenoid that is connected through a closed contact in the solenoid to the cranking motor when the cranking motor solenoid circuit is energizing a coil in the cranking motor solenoid that is forcing the contact in the solenoid closed.
The disconnect switch may assume any of several different embodiments according to further principles of the invention.
Another general aspect of the invention relates to an electrical system in an engine-powered land vehicle. A battery bank comprises one or more D.C. storage batteries. An electric cranking motor draws current from the battery bank to crank the engine at starting when a cranking motor solenoid is energized. A disconnect switch is in circuit between the battery bank and a distribution point for the entire electrical system load except the engine cranking motor. The disconnect switch selectively connects and disconnects the entire electrical system load except the engine cranking motor to and from the battery bank. A switch-free electric circuit provides continuity between the battery bank and the cranking motor solenoid independent of the disconnect switch and carries current for operating the cranking motor. Here too, the disconnect switch may assume any of several different embodiments.
Still another aspect of the invention relates to an electrical system in an engine-powered land vehicle comprising a battery bank comprising one or more D.C. storage batteries and an electric cranking motor that draws current from the battery bank to crank the engine at starting when a cranking motor solenoid is energized. A disconnect switch is in circuit between the battery bank and a main distribution point through which current is delivered from the battery bank to all electrical devices in the electrical system except the cranking motor and a normally open switch that, when operated closed, energizes a solenoid coil that operates the disconnect switch from an OFF position disconnecting all the devices except the cranking motor and the normally open switch from the battery bank to an ON position connecting all the devices except the cranking motor and the normally open switch to the battery bank. A switch-free electric circuit provides continuity between the battery bank and the cranking motor solenoid and carries current for operating the cranking motor and current for energizing the solenoid coil that operates the disconnect switch from OFF position to ON position when the normally open switch is operated closed.
One more aspect of the invention relates to a method for avoiding draining a battery bank of one or more storage batteries in an engine-powered land vehicle to a point where the battery bank is incapable of operating an electric cranking motor to crank the engine at starting while providing a switch-free path for current flow from the battery bank to the cranking motor solenoid during engine cranking. The method comprises placing a disconnect switch that can be operated to respective ON and OFF positions in circuit between the battery bank and multiple circuit protection devices that distribute current to individual circuits in the vehicle, including a cranking motor solenoid circuit through which the cranking motor solenoid is energized to connect the cranking motor solenoid to the battery bank for operating the cranking motor to crank the engine at starting, so that the circuit protection devices are connected to the battery bank when the disconnect switch is in ON position and disconnected from the battery bank when the disconnect switch is in OFF position. The cranking motor solenoid is connected to the battery bank through a switch-free current path for carrying cranking current from the battery bank to the cranking motor via the cranking motor solenoid when the disconnect switch is in ON position and the cranking motor solenoid is being energized by the cranking motor solenoid circuit.
The foregoing, along with further aspects, features, and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. The disclosure includes drawings, briefly described as follows.